My 1968 has late 1980's Vette PBC discs in the rear, and single piston 1969 style discs in the front. After a track day, I realized I had too much front bias. The master & combination valve is a new disc/disc set from Master Power. I noticed there is a junction un the rear brake line under the driver's rocker panel that looks to me like another proportioning valve, or maybe the residual pressure valve from the original drums? I bought the car as is, and did'nt notice the problem until I beat on it on a track. I am thinking I can just replace the junction under the rocker paner with and adjustable prop valve, and it should fix it. Any thoughts? Thanks!

If you have a combo valve you should remove or disable the valve under the rocker, or the combo valve. They both can restrict pressure under hard braking.

You dont want to run 2 valves.

You might not need any.

Thanks - that confirms what I was thinking.

I think the vette rears are so small, you won't need a prop valve at all. A larger rear caliper borae size would be better.
Take a look at the late 80's vette front bore dia and compare that to your 69 ft caliper size, big difference.
David

Thanks for the replies. They are actually late 80's corvette fronts, I'm not exactly sure of the piston size. Hopefully, getting rid of the prop valve under the car will get it balanced. If not, more work.

Thanks.